Batch and Flow-Injection Spectrophotometric Determination of Methyldopa Using Metochlopramide as diazotized Chromogenic Reagent


Abstract New, simple and sensitive batch and Flow-injection spectrophotometric methods for the determination of Methyldopa in pure form and in pharmaceutical preparations were proposed. These methods were based on diazotization and coupling reaction between methyldopa and diazotized metochlopramide in alkaline medium to form an intense orange-red water-soluble dye that is stable and has a maximum absorption at 470nm. A graphs of absorbance versus concentration show that Beer's law is obeyed over the concentration range of 1-14 and 5-130 µg.mL-1 of Methyldopa, with detection limits of 0.15 and 3.213 µg.mL-1 of Methyldopa for batch and FIA methods, respectively. The FIA procedure sample throughput was 70h-1. All different chemical and physical experimental parameters affecting on the development and stability of the colored product were carefully studied and the proposed methods were successfully applied to the determination of Methyldopa in pharmaceutical preparations.